Crimping process



p 26, 6 B. J. GAJJAR 3,343,241 I CCCCCCCCCCCCC SS INVENTOR I BHARATJAYBHADRA GAJJAR BY WM 4% United States Patent ()fiice 3,343,241Patented Sept. 26, 1967 3,343,241 CRIMPING PROCESS Bharat JaybhadraGajjar, Wilmington, Del., assignor to E. I. du Pout de Nemours andCompany, Wilmington, DeL, a corporation of Delaware Filed Apr. 29, 1965,Ser. No. 451,713 6 Claims. (Cl. 28-72) ABSTRACT OF THE DISCLOSURE Aprocess for developing crimp of yarns that have a latent capacity tocrimp when exposed to hot wet processing conditions. The improvementinvolves cooling the yarn immediately prior to the hot wet processingstep.

This invention relates to warp-knitted fabrics having spun-like ortextured properties. It also relates to an improved yarn finishingmethod that can be used for producing such fabrics.

Conventional knitted tricot fabrics, frequently made from rayon orcellulose acetate yarns, have heretofore tended to lack texture, goodhand, and covering power. It has been recognized that pre-texturing ofthe yarns would improve these properties but the filaments employed forthis purpose are of such fine denier that the mechanical quality of thepre-textured yarns is quite poor. As a consequence the use of suchpre-textured yarns would cause excessive breaks in the knittingoperation and would result in fabrics of poor quality. The texturing ofsuch yarns raises still another problem; namely, a problem of economicsowing to the fact that very precise control is required in the texturingof extremely fine denier yarns. This is essential to obtain the gooddenier uniformity needed to make an acceptable product.

One solution for improving the properties of knitted tricot fabrics isthat described in Kasey US Patent 3,041,861 wherein two yarns ofdiffering retractability, i.e., residual shrinkage, are used to form theknitted fabric. However, such fabrics, although considerably improvedwith respect to certain properties, still have no appreciable texture orbulk and hence typically exhibit a rather flat appearance. Then, too,such fabrics also generally lack any appreciable two-directionalstretch, this being a property that would be highly advantageous formany warp-knitted fabrics.

In accordance with the invention there is provided a two-bar,warp-knitted fabric wherein the stitches are formed of first and secondsynthetic filamentary yarns, the ratio of the loop length of said firstyarn to the loop length of the second yarns being 1.1-1.5:1, said firstyarn comprising latently crimpable two-component filaments providing anaverage of 3 to 12 crimps per stitch length when the fabric is finishedby scouring at the boil. Upon treating such a fabric to develop thelatent crimpability of the two-component filamentary yarn, the fabrictakes on a spun-like or textured character somewhat resembling cottonfabrics. Moreover, owing to the high degree of crimp in the treatedfabric, improved covering power and an appreciable degree of two-waystretchability are provided. It is to be understood that either one orboth of the two yarns comprising the warp-knitted fabric, abovedescribed, may be formed of latently crimpable two-component filamentsand that it is only essential that the stated ratio of the loop lengthof one yarn to that of the second yarn is fulfilled.

The novel warp-knitted fabrics of the invention are conveniently knittedon an ordinary knitting machine by feeding one of the two yarns at thetop front bar of the machine and by feeding the second of the yarns atthe bottom back bar of the machine. The yarn composed of latentlycrimpable two-component filaments may be fed to either the top front baror to the bottom back bar or to both bars of the machine. The relativetensions upon the yarns fed to the machine are adjusted so that one ofthe yarns, specifically a yarn composed of latently crimpabletwo-component filaments, forms loops which are larger than those of theother yarn. The larger loops of the stitches are formed so as to have aloop length which is 1.1 to 1.5 times the loop length of the secondyarn. Ordinarily this can be achieved in a Jersey fabric if the fabricis knitted in such a manner that the bicomponent front bar to regularback bar actual knitting ratio is at least 1.38, preferably 1.45.

The novel fabrics of the invention will be further understood byreference to the drawings wherein:

FIGURE 1 is a loop diagram of a conventional prior art greige orfinished tricot fabric in which the yarns of the top bar and yarns ofthe bottom bar have the same loop length. The yarns lay on top of oneanother, thus giving a fabric which was poor transmitted light coverbecause of the relatively large holes through which light can pass.

FIGURE 2 is a loop diagram of the front of a greige tricot fabric(Jersey stitch) of this invention prior to crimp development.

FIGURE 3 illustrates the appearance of the fabric of FIGURE 2 followingdevelopment of crimp.

In the fabric stitch shown in FIGURE 2, yarn 3 forms the larger loop andis therefore comprised of the latently crimpable two-componentfilaments. The loop length of yarn 4 is considerably smaller and thismay or may not be formed of latently crimpable two-component filaments.The loop length of yarn 3 is the distance from point a, around the loop,and back to that point. Similarly the loop length of yarn 4 is thedistance from point 12, around the loop, and back to that point. Theloop length of the yarns may be determined using a microscope andmeasuring the indicated distances.

In FIGURE 3, the crimped configuration of yarn 3 in the stitches can beobserved. It will be apparent that such stitches will provideconsiderably improved covering power as compared to the prior art fabricof FIG- URE 1. If yarn 3 had not initially been formed into largerloops, the tendency thereof to fully crimp would have been prevented bythe other loops which it engages. As illustrated in FIGURE 3, yarn 3 hasan average of 7 even crimps per stitch length.

A fabric of the invention, as illustrated in FIGURE 3, has superiorbulk, thickness and cover at a given weight as compared to non-texturedwarp-knitted fabrics of the prior art. In addition to also exhibiting atextured quality similar to cotton fabrics, this fabric after bleachingand drying further shows a two-way elongation-potential (stretch) whichis at least 50% greater (both in the wale direction and in the coursedirection) than a prior art fabric.

By the term latently crimpable as used herein to describe the filamentscomprising the bicomponent yarns used in this invention, it is meantthat although the filaments to be knitted are in a generally straightcondition they nevertheless possess an inherent tendency to take on orotherwise assume an irregular contorted configuration by scouring at theboil, e.g., by exposure thereof to water at 100 C. The fibers should becapable of not merely assuming a generally curved or flexed shape but,rather, of affording a crimp frequency sufliciently high to give 3 to 12crimps per stitch length. This is important if the fabric is to exhibitgood bulk and aesthetics. It will be understood that in the final fabricthe crimped fibers will be seen to possess a curved or curledconfiguration. In other words such fibers will trace a bend or gradualchange in direction as opposed to many types of mechanically crimpedfibers which exhibit an abrupt change in direction, e.g. the well knownstuffer-box or saw-tooth crimped configuration.

The latently crimpable synthetic filaments of the yarns employed in thepractice of the invention will be composed of either linear condensationpolymers or linear addition polymers, for example, acrylonitrilepolymers and copolymers; polyamides, such as polyhexamethyleneadipamide, polycaproamide, poly(meta-phenylene isophthalamide), andcopolyamides; polyesters such as polypivalolactone, polyethylene terehthalate and copolyesters prepared from glycols and terephthalic andisophthalic acids; polyethylene and ethylene copolymers; polypropyleneand propylene copolymers; polybenzimidazole; copolymers of acrylonitrilewith small amounts of copolymerizable monomers (e.g. with 12% by weightmethyl methacrylate or with 10% by weight vinyl acetate); and the like.In any case the latent capacity to crimp is built into the fiber bysuitable selection of the individual components. Suitable techniques forpreparing two-component fibers with latent crimp are described in US.patent to Taylor 3,038,237 and in British Patent 950,429. In oneembodiment the two-component filaments may comprise two continuouscomponents adhered to one another in side-to-side relationship alongtheir length. Alternatively they may comprise a sheath component and acore component. A preferred class of filaments is that described in theaforementioned British patent wherein one component is a homopolyamideand the other is a copolyamide. Preferably the bicomponent fibers willretract, i.e. shrink, less than 5% in length upon scouring at the boil.

One of the yarns of the novel fabric of the invention will be composedof latently crimpable two-component filaments of the class describedabove. The other yarn may be identical, of the same class or of ordinarymonocomponent synthetic filaments.

A corollary finding of this invention pertains to an improved method fordeveloping the crimp of yarns comprising two-component filament thathave a latent capacity to crimp when exposed to hot wet processingconditions. The improvement involves cooling the yarn in the presence ofwater to below C. immediately prior to crimping under essentially notension by exposure to a heated aqueous fluid at a temperature of atleast about 100 C. Although the reasons for this unexpected im-'provement are not fully understood, it appears that the drastic changein the fiber temperature upon going from a very cold to a very hotcondition causes a pronounced shock effect which in turn markedlyincreases the degree of crimp and bulk beyond that would otherwise Thecooling of the fibers prior to crimp development according to thisimproved process should be sufficient to lower the fiber temperature tobelow 10 C. and preferably to 0 C. or below. The fibers should beexposed to water, either as a liquid or ice, at the low temperature.Cooling in an ice-water bath is especially desirable. There should be noappreciable time delay between the cooling and heating steps for fullrealization of this improved crimping procedure.

The development of crimp is effected by exposing the yarn comprisingtwo-component filaments to a heated aqueous fluid at a temperature of atleast about C. The heated aqueous fluid may be in the form of hot wateror steam, either saturated or not but preferably the temperature of thefilaments is raised essentially instantaneously, e.g. by plunging into abath of boiling water. Textile lubricants or other additives mayadvantageously be included in the fluid. It will be understood thatcrimp development must occur while the fibers are under essentially notension, otherwise maximum bulkiness will not be realized.

The shock cooling-heating procedure, above described, is particularlydesirable for developing crimp in the novel warp-knitted fabrics of thisinvention. However, it will be apparent that it can also be used toadvantage for development of crimp in any product comprising latentlycrimpable two-component filaments. Woven, nonwoven, and other forms ofknit fabrics comprising such yarns of such filaments will also derive anenhanced bulk by the use thereof. It will be understood that any fabricto be so treated should be of a generally loose or open construction sothat crimp development can freely occur.

In lieu of cooling the two-component filaments prior to crimpdevelopment, they may be treated with certain organic solvents such asbenzyl alcohol, to also realize improved bulk. For most purposes this isdisadvantageous, however, because of the problems associated withhandling such materials.

The following examples are given to illustrate the invention, and arenot intended to limit the scope thereof in any manner.

Example I A 30 denier, 14 bicomponent (trilobal cross section) heatcrimpable filament yarn is used in conjunction with a 30 denier, 10monocomponent (trilobal cross section) filament non-heat crimpable yarnto knit a tricot fabric (Fabric No. 1 on Tables I and II below) on a 28gauge, 84 inch wide machine using a Jersey pattern (2-3, 1-0 front barand l-0, 1-2 back bar stitch), 5" Quality, and front runner 54" backrunner 38.5" for a 1.4 knitting ratio. Each filament of the 14 filamentyarn consists of two continuous, adherent, eccentric components, onecomponent (50% of the filament weight) being a sheath ofpoly(hexamethylene adipamide) and the second component (the other 50% ofthe filament weight) being a core of a copolyamide of hexamethyleneadipamide and hexamethylene isophthalamide (70:30 weight ratio of therespective repeating units). Each filament of the 10 filament yarnconsists of poly(hexamethylene adipamide). The greige fabric so knittedis 15.0 mils thick, has a density of 2.50 ounces per square yarn, andhas a bulk of 4.49 cubic centimeters per gram. One piece of the knitfabric is kept in an ice-water bath at 33 F. for 10 minutes. Then thiscold piece and a second (identical, but untreated with ice-water) pieceare immediately dropped in boiling water and kept there for /2 hour. Thetwo pieces are then removed and tumble dried. Tumble drying inlaboratory is usually accomplished in a conventional domestic clothesdryer for 30 minutes at about F. As shown in Table I, similar fabricsare prepared and then processed in the same Way. Properties of thevarious fabrics so obtained are shown on Table II.

TABLE I.FABRIC CONSTRUCTION Fabric Filament Stitch Quality in Length ofNo. Fabric Layout Composition 1 Design inches 1 yfilfil in inc es 3 JFront bar: 30 denier, 14 bicomponent trilobal filament yarn 66/]66/612-3, 1-0 5 54 \Back bar: 30 denier, 10 monocomponent trilobal filamentyarn 66 38. 5 Front bar-same as fabric 5 55. 5 Back bar-same as fabric#1"... 39. 25 {Front barsame as fabric #1 7 57. 5 Back bar-same asfabric #1.- 41.0

1 66//66/6I= Poly(hexamethylene adipamide) in the sheath (50% offilament weight) and a copolyamide of hexamethylene adipamide withhexamethylene isophthalamide (70:30 weight ratio of the respectiveunits) in the core (50% of the filament weight); 66=

Poly(hexamethylene adipamide); 66//66/6=Poly(hexamethylene adipamide) inthe sheath (50% amide of hexamethylene adipamide with caproamide (7 :30weight ratio of the respective units) 2 Quality is the distance occupiedby a 480 course rack. 3 Length 0' yarn required to form a 480 courserack.

of filament weight) and a copolyin the core (50% of filament weightNOTE: It should be noted that for eac 1 fabric, the yarn comprisingbicomponent filaments forms a knit loop larger than the knit loop ofmonocomponent filaments, since the length of bicomponent filament yarnrequired to form a 480 course rack is greater than the length ofmonoeomponent yarn required to form a 480 course rack.

TABLE II.-F.ABRIC PROPERTIES Greige Fabric After Finishing Process A.After Finishing Process B Fiagoric Thickness, Weight, Bulk, Thickness,Weight, Bulk, Thickness, Weight, Bulk,

Mils Oz./sq. yd. cc./gm. MllS Oz./sq. yd. ccJgm. Mils 0z./sq. yd.cc./gm.

Similar results are achieved with a fabric comprising front bar yarn offilaments consisting essentially of poly (hexamethylene adipamide) inthe sheath (50% of filament weight) and a core (50% of filament weight)of a copolymer of hexamethylene adipaimide with hexamethylene sebacamide(70:30 weight ratio of the respective units).

Finishing Process A is as described above comprising a freeze treatmentdirectly followed by a hot treatment and then tumble drying. FnishingProcess B is the same as Finishing Process A except that no freezetreatment is effected.

Both fabrics are highly satisfactory but that processed according toProcess A not only has superior bulk, thickness, and cover at a givenweight, but also unexpectedly has a most attractive cotton-likeappearance and texture. Furthermore, when each of the fabrics hassubsequently been heat set, bleached and finally dried, they show atwo-way elongation-potential (stretch) that is more than 50% greater(both in the wale direction and in the course direction) than thetwo-way elongation-potential of a conventional tricot fabric. Thefabrics processed according to process A, however, exhibit bettertwo-way elongation-potential than do the fabrics processed according toProcess B.

Example II Seven skeins are provided of 15 denier, one (round crosssection) bicomponent filament =yarn, each filament being of sheath-coreconstruction with a sheath of essentially poly-(hexamethylene adipamide)(50% of filament weight) and a core (50% of filament weight) ofessentially a copolyamide of hexamethylene adipamide with hexamethylenesebacarnide (70:30 weight ratio of respective units). The length of eachskein is measured under zero tension.

Five of these skeins are added to a hot-water bath at 140 F. and 'keptat 140 F. for /2 hour. Then one skein is taken out, and the water-bathis raised to 160 F. and kept at 160 F. for /2 hour. Next, a second skeinis taken out, and the water bath is raised to 180 F. and kept at 180 F.for /2 hour. Then a third skein is taken out, and the water bath israised to 200 F. and kept at 200 F. for /2 hour. A sixth skein is keptin ice for /2 hour. Finally, a fourth skein is removed from the waterbath, and the water bath is raised to the boil.

Then a seventh skein along with the sixth skein is placed in the boilingwater bath which contains three skeins: Nos. 5, 6 and 7. The threeskeins are taken out of the water bath at the end of a /2 hour. Thelength of each of the seven skeins are measured after each is removedfrom the hot-water bath. The amount the skeins are reduced in length,i.e., from one end to the other, indicates the degree of crimping whichhas occurred. Table III shows the results of all measurements.

1 Added at room temp. I Added aiter freeze treatment.

It is significant that skein 5, which has been gradually brought up tothe boil, undergoes a reduction in length of only 19.6% whereas skein 6,which has been rapidly plunged into boiling water, undergoes a reductionin length of 27.0%. Even more significantly, skein 7 which has firstbeen thoroughly chilled and then plunged into boiling water undergoes areduction in length of 35.8%.

The warp-knitted fabrics of the invention are useful for undergarments,sleepwear, gloves, sport shirts, and other types of apparel, as well asfor knit hosiery.

Many other equivalent modifications will be apparent to those skilled inthe art and, therefore, this invention is not intended to be limitedexcept as indicated in the appended claims.

What is claimed is:

1. In a process for crimping a synthetic yarn composed of two-componentfilaments, said filaments having a latent capacity to crimp when treatedby hot wet processing conditions, by the step of exposing said filamentswhile under essentially no tension to a heated aqueous fluid at atemperature of at least about C.; the improvement, for increasing thebulk of the crimped yarn, comprising cooling the yarn in the presence ofwater to below about 10 C. immediately prior to said exposure to theheated aqueous fluid.

2. Process according to claim 1 wherein the yarn is in the form of aknit fabric.

3. Process according to claim 1 wherein the cooling of the yarn isconducted in an ice-water bath at about 0 C. or below.

4. Process according to claim 1 wherein the yarn is completely immersedin said aqueous fluid immediately after cooling, thereby raising thetemperature of the filaments to at least about 100 C. essentiallysimultaneously.

5. Process according to claim 1 wherein the twocomponent filaments aresheath-core filaments, the sheath comprising polyhexamethyleneadiparnide and the core comprising a copolymer of hexamethyleneadipamide and .hexamethylene isophthalamide.

References Cited UNITED STATES PATENTS 2,289,377 7/1942 Miles 8130.12,880,056 3/1959 Carr et a1. 264168 2,931,091 4/1960 Breen 28-723,017,686 1/1962 Breen et a1. 161-180 3,041,861 7/1962 Kasey 66195MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Assistant Examiner.

1. IN A PROCESS FOR CRIMPING A SYNTHETIC YARN COMPOSED OF TWO-COMPONENTFILAMENTS, SAID FILAMENTS HAVING A LATENT CAPACITY TO CRIMP WHEN TREATEDBY HOT WET PROCESSING CONDITIONS, BY THE STEP OF EXPOSING SAID FILAMENTSWHILE UNDER ESSENTIALLY NO TENSION TO A HEATED AQUEOUS FLUID AT ATEMPERATURE OF AT LEAST ABOUT 100*C.; THE IMPROVEMENT, FOR INCREASINGTHE BULK OF THE CRIMPED YARN,